For indications such as abdominal aortic aneurysms, traditional open surgery is still the conventional and most widely-utilized treatment when the aneurysm's size has grown to the point that the risk of aneurysm rupture outweighs the drawbacks of surgery. Surgical repair involves replacement of the section of the vessel where the aneurysm has formed with a graft. An example of a surgical procedure is described by Cooley in Surgical Treatment of Aortic Aneurysms, 1986 (W.B. Saunders Company).
Despite its advantages, however, open surgery is fraught with high morbidity and mortality rates, primarily because of the invasive and complex nature of the procedure. Complications associated with surgery include, for example, the possibility of aneurysm rupture, loss of function related to extended periods of restricted blood flow to the extremities, blood loss, myocardial infarction, congestive heart failure, arrhythmia, and complications associated with the use of general anesthesia and mechanical ventilation systems. In addition, the typical patient in need of aneurysm repair is older and in poor health, facts that significantly increase the likelihood of complications.
Due to the risks and complexities of surgical intervention, various attempts have been made to develop alternative methods for treating such disorders. One such method that has enjoyed some degree of success is the catheter-based delivery of a bifurcated stent-graft via the femoral arteries to exclude the aneurysm from within the aorta.
Endovascular repair of aortic aneurysms represents a promising and attractive alternative to conventional surgical repair techniques. The risk of medical complications is significantly reduced due to the less-invasive nature of the procedure. Recovery times are significantly reduced as well, which concomitantly diminishes the length and expense of hospital stays. For example, open surgery requires an average six-day hospital stay and one or more days in the intensive care unit. In contrast, endovascular repair typically requires a two-to-three day hospital stay. Once out of the hospital, patients benefiting from endovascular repair may fully recover in two weeks while surgical patients require six to eight weeks.
Despite these and other significant advantages, however, endovascular-based systems have a number of shortcomings. Present bifurcated stent-grafts require relatively large delivery catheters, often up to 24 French and greater in diameter. These catheters also tend to have a high bending stiffness. Such limitations result in the need for a surgical cut-down to deliver the stent-graft and make delivery through the often narrow and irregular arteries of diseased vessels difficult and risky. Because of this, endovascular treatment of aortic aneurysmal disease is not available to many patients who could otherwise benefit from it. For instance, women statistically tend to have smaller vessels and therefore some are excluded from many current endovascular therapies simply due to this reason. There is therefore a need for an endovascular stent-graft capable of being delivered via a smaller and more flexible delivery catheter. Even greater advantages may be realized if such an endovascular stent-graft is capable of being delivered percutaneously.
Further, an endovascular stent-graft must withstand tremendous pulsatile forces over a substantial period of time while remaining both seated and sealed within the vessel. In order to achieve these objectives, the device, which may comprise component parts and/or materials, must remain intact. The device must resist axial migration from the site of deployment while being subjected to significant pulsatile forces, and it should have sufficient radial compliance to conform to the vessel anatomy within which it is deployed so as to prevent blood leakage between the device and the vessel wall at both its proximal, or cephalic, end as well as at its distal, or caudal end or ends (where the net force may be retrograde). Such a device should conform to the morphology of the treated vessel, without kinking or twisting, over the life of the patient.